Phosphatidylinositol (hereinafter abbreviated as “PI”) is one of a number of phospholipids found in cell membranes. In recent years it has become clear that PI plays an important role in intracellular signal transduction. In the late 1980s, a PI3 kinase (PI3K) was found to be an enzyme which phosphorylates the 3-position of the inositol ring of phosphatidylinositol (D. Whitman et al, 1988, Nature, 332, 664).
PI3K was originally considered to be a single enzyme, but it has now been clarified that a plurality of subtypes are present in PI3K. Each subtype has its own mechanism for regulating activity. Three major classes of PI3Ks have been identified on the basis of their in vitro substrate specificity (B. Vanhaesebroeck, 1997, Trend in Biol. Sci, 22, 267). Substrates for class I PI3Ks are PI, PI 4-phosphate (PI4P) and PI 4,5-biphosphate (PI (4,5)P2). Class I PI3Ks are further divided into two groups, class Ia and class Ib, in terms of their activation mechanism. Class Ia PI3Ks include PI3K P110α, p110β and p110δ subtypes, which transmit signals from tyrosine kinase-coupled receptors. Class Ib PI3K includes a p110γ subtype activated by a G protein-coupled receptor. PI and PI(4)P are known as substrates for class II PI3Ks. Class II PI3Ks include PI3K C2α, C2β and C2γ subtypes, which are characterized by containing C2 domains at the C terminus. The substrate for class III PI3Ks is PI only.
In the PI3K subtypes, the class Ia subtype has been most extensively investigated to date. The three subtypes of class Ia are heterodimers of a catalytic 110 kDa subunit and regulatory subunits of 85 kDa or 55 kDa. The regulatory subunits contain SH2 domains and bind to tyrosine residues phosphorylated by growth factor receptors with a tyrosine kinase activity or oncogene products, thereby inducing the PI3K activity of the p110 catalytic subunit which phosphorylates its lipid substrate. Thus, the class Ia subtypes are considered to be associated with cell proliferation and carcinogenesis.
It has been extensively published that the morpholino derivatives shown in Formula I below are PI3K inhibitors:

Wherein Cy is an unsaturated or aromatic, mono or fused ring. Some of the representative examples are listed below: LY294002 (Vlahos et al. J. Biol. Chem. 1994, 269, 5241-5248), Ia (WO2007/129161), Ib (WO2007/084786), Ic (WO2007/080382), Id (WO2007/042810), TGX221 (WO2004/016607), and Ie (WO2008/018426).

In the above examples, the morpholine group was considered essential for the PI3K inhibitory activities. In WO2007/132171, the morpholine group was replaced by a heteroaryl group.
More recently, we (U.S. provisional application Ser. No. 61/134,163, WO2010/005558) and others (WO 2009/045174, WO 2009/04575) found that compounds of Formula II are also potent PI3K inhibitors.

Furthermore, we discovered that compounds of Formula III are potent and selective PI3Kδ inhibitors, some with >10 fold selectivity against PI3Kδ verses other Class 1 PI3K isoforms, particularly when
is 2-difluoromethyl-benzoimidazol-1-yl.

Subsequently, we further discovered that compounds of Formula IIa are also potent and selective PI3K, mTOR inhibitors with better pharmaceutical properties than the corresponding compounds of Formula II. Similarly, it was discovered that compounds with 2-difluoromethyl-benzoimidazol-1-yl substitution are potent and selective PI3K delta inhibitors (U.S. provisional application Ser. No. 61/214,828, WO2010/056320).

Compounds with 2-difluoromethyl-benzoimidazol-1-yl substitution to a monocyclic heteroaryl have been published in a few patents (see e.g. WO 2008032072, WO 2008032027, WO 2008032060, WO 2008032036, WO 2008032033, WO 2008032089, WO 2008032091, WO 2008032086, WO 2008032028, WO 2008032064, WO 2008032077, and WO 2008032041). But those compounds were not disclosed as potent and selective PI3Kδ inhibitors. In fact, a representative compound, ZSTK474 was reported to be a pan-PI3K inhibitor with limited (<10 fold) selectivity against PI3Kδ (Yaguchi et al. Journal of the National Cancer Institute, 98 (8), 545, 2006).

This invention further extends our search for more potent and selective PI3Kδ inhibitors according to Formula III and other bicyclo heteroaryls. Surprisingly, we found that certain substitutions of Formula III lead to compounds with different PI3K kinase selectivity profiles.
PI3Kδ is preferentially expressed in cells of hematopoietic origin. In mice carrying PI3Kδ null or catalytically inactive mutations, defects in B cell functions such as BCR-mediated signaling, response to antigens, and reduced levels of circulating immunoglobulins have been reported. PI3Kδ plays an essential role in certain signaling pathways of neutrophil activation and appears to be an attractive target for the development of an anti-inflammatory therapeutic (Sadhu et al. Biochem. Biophys. Res. Communications 308, 764, 2003). It was also found to be required for optimal IgE/Ag-dependent hypersensitivity responses in mice, suggesting that it is a potential therapeutic target for allergy- and mast cell-related diseases such as asthma (Ali et al. J. Immunology, 180, 2538, 2008; Park et al. Respirology 13, 764, 2008). Furthermore, the expression pattern of PI3Kδ and its effects in B-lymphoid cells have raised hopes that specific inhibitors of PI3Kδ may suppress the proliferation and survival of transformed hematopoietic cells. Indeed, high levels of PI3Kδ have been found in leukemic cells from patients with acute myeloid leukemia (AML) (Sujobert et al. Blood, 106, 1063, 2005), thereby suggesting that it is also a potential target for treating leukemia.